Peter Gustav Lejeune Dirichlet

He married Rebecka Mendelssohn, the daughter of a prominent Jewish banker, in 1832. The couple had two children.

He suffered a heart attack in the summer of 1858. Even though he survived the attack, his health deteriorated badly thereafter and he died on 5 May 1859.

Peter Gustav Lejeune Dirichlet was born on 13 February 1805 in Düren—the town was part of the French Empire at that time—to Johann Arnold Lejeune Dirichlet and his wife Anna Elisabeth. His father was a postmaster, merchant, and city councilor.

Peter Gustav Lejeune Dirichlet hailed from a family of modest means and was the youngest of the seven children of his parents.

He displayed a keen interest in mathematics from an early age. He loved the subject so much that he bought books on the subject with his pocket money as a young boy.

Initially his parents had hoped that he would grow up to be a merchant, but the boy’s fascination with mathematics was so much that they finally gave in to his wishes and let him pursue higher studies in mathematics. They sent him to the Gymnasium in Bonn in 1817 when he was 12 years old.

After studying at Bonn for three years he moved to the Jesuit Gymnasium in Cologne in 1820 where he was taught by the mathematician Georg Ohm. This helped him widen his mathematical knowledge though he could not learn much because of his inability to speak fluent Latin.

Peter Gustav Lejeune Dirichlet began his research during his student days and his first original research comprised part of a proof of Fermat's last theorem. This work brought him immediate fame as a budding mathematician, and in 1825 he was appointed to lecture at the French Academy of Sciences. He was only 20 years old at that time and had no degree!

He decided to return to Germany in November 1825. However, in order to teach in a German university he needed an habilitation which he did not have. Also the fact that he could not speak Latin was another problem.

The University of Cologne awarded him an honorary doctorate in February 1827 and the Minister of education granted him a dispensation for the Latin disputation required for the Habilitation. Thus he earned his habilitation without much difficulty and lectured in 1827–28 at Breslau.

He found the academic standards at Breslau to be low and hence moved to Berlin in 1828. He worked at the Military College and was also appointed a professor at the University of Berlin the same year. He taught at the university till 1855, while continuing with his job at the Military College.

In 1832, Dirichlet became a member of the Prussian Academy of Sciences; he was the youngest member and was only 27 years old at the time.

Peter Gustav Lejeune Dirichlet is primarily remembered for his contribution to the field of number theory. He created the branch of analytic number theory, introduced the Dirichlet characters and L-functions, and proved the Dirichlet unit theorem, a fundamental result in algebraic number theory.